1. Field of the Invention
The present invention relates to a structure and a manufacturing method of an inversed microphone module and a microphone chip component.
2. Description of Related Art
Along with the personalization and popularization of global communication, it has become very common that everybody has at least one mobile phone. Due to the requirement of parenthood, even school children have mobile phones, thus, the age of mobile phone's consumer group is greatly reduced to be below 10.
Moreover, according to a report issued by Topology Research Institute (TRI) in September, 2005, global production of mobile phones in 2005 is about 760 millions, and the number of mobile phone users is up to 1.685 billions. According to TRI's estimation, global mobile phone users will be up to 2.236 billions in 2009. Obviously, the size of mobile phone market is very large.
Nowadays, for the convenience of usage, a microphone for camera function is further disposed in a mobile phone besides the microphone for conversing. Accordingly, the requirement to microphone is increased along with the increase in requirement to video/audio function.
A microphone module manufactured with micro electro-mechanical system (MEMS) has small thickness and volume, and surface mount process can be performed thereto through solder reflow. Thus, to meet the requirements of small volume and low coat of mobile phones, microphone module of smaller volume is gradually taking up the market of electric condenser microphone (ECM).
In addition, the microphone module manufactured with MEMS has low power consumption (160 uA), thus, the power consumption thereof is only about ⅓ of ECM. Since a mobile phone has limited electricity storage, such advantage of MEMS microphone module urges the ECM microphone to be replaced by MEMS microphone module.
As to other products equipped with microphones, the requirement to MEMS microphone module is also increasing. For example, MEMS microphone module is being applied to portable audio player and digital camera having micro drive (MD) or flash memory. Accordingly, MEMS microphone module may has remarkable market occupancy in foregoing applications.
An existing ECM microphone module will be described. Refer to FIG. 1, which is a cross-sectional view of a conventional Knowles microphone module.
Generally, the microphone chip 10 has an acoustic sensing portion 12. The microphone chip 10 and the logic chip 20 are electrically coupled to the bottom plate 30. The supporting ring 40 and the top plate 50 are sequentially stacked on the bottom plate 30 by using conductive compound 32. The top plate 50 has an opening 52 which allows acoustic wave to pass through.
The space from the opening 52 to the acoustic sensing portion 12 is referred to as a front acoustic cavity. The space from the acoustic sensing portion 12 to the bottom plate 30 is referred to as a back acoustic cavity.
In the Knowles microphone module, supporting ring 40, top plate 50, bottom plate 30, microphone chip 10, and logic chip 20 form the front acoustic cavity V1 (referring to FIG. 2), and acoustic sensing portion 12 and microphone chip 10 form the back acoustic cavity V2.
In the front acoustic cavity V1, liquid compound 34 is dispensed on the logic chip 20 through a dispensing process for protecting the logic chip 20 and the connection joins thereof to the bottom plate 20. The liquid compound 34 cannot be dispensed onto the microphone chip 10 for once the liquid compound 34 is dispensed onto the microphone chip 10, it may flow to the acoustic sensing portion 12 so that the performance of the microphone module may be affected.
Besides, from the point of acoustics, the relationship between the front acoustic cavity and the restraining frequency is as following according to Helmholtz theorem:
                              f          e                =                              c                          2              ⁢              π                                ⁢                                    s                              Vl                e                                                                        (                  Expression          ⁢                                          ⁢          1                )            
In expression 1, V represents the volume of the front acoustic cavity, and fe represents the restraining frequency. The restraining frequency shows the acoustic sensing range of the microphone module and which is the larger, the better. In other words, the volume of the front acoustic cavity is the smaller, the better. The back acoustic cavity is a space provided for the transfiguration of acoustic sensing portion 12, thus, it is the larger, the better.
In overview, the conventional technique has at least following disadvantages:
(1) the microphone chip is disposed within the acoustic cavity and is not protected by sealing compound, thus, the reliability of the microphone module is low, and if the microphone module falls to ground (for example, a mobile phone is dropped to the ground), the microphone module may be damaged since the solder joints of the microphone chip are not protected by sealing compound.
(2) The dispensing process is time-consuming, thus, it is difficult to increase the production throughput.
(3) The acoustic cavity is defined by stacking supporting ring and top plate, thus, the structure of the entire microphone module is not compact enough and the volume thereof cannot be reduced, and furthermore, the volume of the front acoustic cavity cannot be reduced, which results in small acoustic sensing range of the microphone module.